Batch type vertical hot wall depressurizing CVD apparatus are widely used in IC manufacturing methods in film-forming processes for forming CVD films such as silicon nitride (Si3N4) or silicon oxide and poly-silicon on semiconductor wafers (hereinafter called “wafers”) on which integrated circuits including semiconductor devices are fabricated.
A process tube is installed vertically inside this batch type vertical hot wall depressurizing CVD apparatus (hereinafter called “CVD apparatus”). The process tube is made from an inner tube that forms the processing chamber and an outer tube that encloses the inner tube.
A heater unit for heating the processing chamber is installed outside the process tube. A gas supply pipe for supplying film forming gas as the process gas into the processing chamber, and an exhaust pipe for vacuum-exhausting the processing chamber are each connected to a manifold that supports the process tube.
A standby chamber is formed below the process tube. A boat elevator for lowering and raising the boat via a seal cap is installed in this standby chamber. The seal cap is structured so as to open and close the opening in the lower end of the process tube by raising and lowering of the boat elevator. The boat is installed vertically on the seal cap. The boat is structured to maintain each of the multiple wafers horizontally while arrayed perpendicularly along the center.
The boat is then loaded into the processing chamber from the bottom opening of the process tube while holding the multiple wafers arrayed perpendicularly. The gas supply pipe supplies film-forming gas into the processing chamber in a state where the furnace is sealed by the seal cap and the heater unit heats the processing chamber. A CVD film is deposited on the wafer. (See for example, patent document 1)    Patent document 1: Japanese Patent Non-Examined Publication No. 2002-110556
Usually, in heat treatment apparatus such as CVD apparatus, the processing chamber is purged with nitrogen gas after heat treatment and the temperature is lowered to a specified temperature, and then the boat is unloading from the processing chamber.
Lowering the temperature is necessary because it prevents a phenomenon where if the boat is unloaded while still at processing temperature, a large temperature differential occurs between wafers and a large temperature differential occurs within the wafer surface which adversely affects the IC device characteristics.
In heat treatment apparatus of this type in the prior art, a gas supply pipe whose spray port is positioned lower than the boat is clamped to a manifold and this gas supply pipe supplies nitrogen gas into the processing chamber.